Configuring data registers to program a programmable device with a configuration bit stream without phantom bits

ABSTRACT

Techniques and mechanisms dynamically configure shift registers among registers composing data registers in a circuit such as a Programmable Logic Device (PLD). A configuration bit stream used to configure the PLD may have a reduced size if “phantom bits” not corresponding to configuration elements are removed. Shift registers may be dynamically configured such that registers which do not correspond to physical configuration elements may be skipped. Thus, a PLD may be programmed with a configuration bit stream without phantom bits.

TECHNICAL FIELD

The present disclosure generally relates to integrated circuits. Morespecifically, the present disclosure relates to systems and methods forconfiguring a circuit using a configuration bit stream.

DESCRIPTION OF RELATED ART

A PLD is a semiconductor integrated circuit which contains logiccircuitry and routing that may be configured to perform a host of logicfunctions. In a typical scenario, a designer uses electronic designautomation (EDA) tools to create a design. The EDA tools create aconfiguration bit stream corresponding to the design. The configurationbit stream is used to configure or program configuration elements withinthe PLD in order to implement the desired functionality and routing.Configuration elements may include non-volatile memories (e.g., flash,antifuses, fuses) and/or volatile memories (e.g., static random-accessmemory (SRAM)) distributed throughout the PLD.

If the configuration elements are non-volatile memories, theconfiguration elements must be configured according to the configurationbit stream upon power-up of the PLD. Conventionally, bits from theconfiguration bit stream are loaded group-by-group into Data Registers.After the Data Registers are loaded with a group of bits, AddressRegisters are used to program or configure a particular group (e.g., asingle column) of configuration elements corresponding to the bits inthe configuration bit stream that are loaded into the Data Registers.However, not all of the locations created by the Data Registers andAddress Registers correspond to a physical configuration element.Accordingly, a plurality of “phantom bits” which do not correspond to aphysical configuration element, but which are still needed to properlyload the Data Registers, are distributed throughout the configurationbit stream.

Removal of the phantom bits may reduce the size of the configuration bitstream. Reducing the size of the configuration bit stream provides amultitude of advantages. Reduction of the configuration bit streamallows a smaller memory device to be used to store the configuration bitstream for PLDs with non-volatile configuration elements. For example, aPLD with on-chip flash storage to hold the configuration bit stream mayrequire less flash memory to store the configuration bit stream. Usingless flash memory may lead to higher yield rates, and therefore, reducedcosts. Additionally, reducing the configuration bit stream size mayallow multiple configuration bit streams to be stored in the samestorage device. The multiple designs may be used in dual booting orpartial reconfiguration of the PLD.

Conventional methodologies to reduce the size of the configuration bitstream are limited. For example, the configuration bit stream may becompressed and stored. However, compression is dependent upon thepattern of “1's” and “0's” in the configuration bit stream. Becausedifferent designs will have different configuration bit streams withdifferent patterns, compression ratios for configuration bit streamswill vary. Accordingly, a worst case compression ratio must be used inorder to determine a flash memory size to store the configuration bitstream. Additionally, a compressed bit stream must be decompressedbefore configuring the PLD, a process which may significantly increasethe total configuration time.

SUMMARY

The techniques and mechanisms of the present disclosure dynamicallyconfigure shift registers among registers composing data registers in acircuit, such as PLDs (including FPGAs, CPLDs, etc.), structured ASICs,ASICs, and other types of devices. The invention is primarily describedwith reference to PLDs as an example of a configurable circuit, but isnot necessarily limited to PLDs.

The present invention provides improved mechanisms for using a smallerconfiguration bit stream which may be used to configure the PLD. In oneexample, a control block may receive a configuration bit stream without“phantom bits” which do not correspond to physical configurationelements. The control block may dynamically configure shift registersamong the data registers such that the configuration bits may beproperly loaded into the configured shift registers. Accordingly, thePLD may be configured. For instance, the control block may receiveinformation from a header portion of the configuration bit streamincluding information regarding configuration bits. The control blockmay configure multiple shift registers of particular lengths andlocations among the data registers such that registers which do notcorrespond to physical configuration elements may be skipped, andtherefore, not part of a configured shift register. Thus, aconfiguration bit stream without phantom bits may be used to configurethe PLD.

These and other features will be presented in more detail in thefollowing specification of the invention and the accompanying figures,which illustrate by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, whichillustrate specific embodiments of the present invention.

FIG. 1 illustrates one example of a design of a PLD and distributions ofaddress locations and physical configuration elements for a particularresource type according to an exemplary embodiment.

FIG. 2 illustrates another example of distributions of address locationsand physical configuration elements for a different resource typeaccording to an exemplary embodiment.

FIG. 3A illustrates an example of a distribution of address locationswithin a PLD according to an exemplary embodiment.

FIG. 3B illustrates an example of a distribution of address locationsand physical configuration elements within a PLD according to anexemplary embodiment.

FIG. 4 illustrates an example of Hard IP blocks affecting a distributionof physical configuration elements and resources within a PLD accordingto an exemplary embodiment.

FIG. 5 illustrates an example of removing “phantom bits” from aconfiguration bit stream according to an exemplary embodiment.

FIG. 6 illustrates an example of a system for loading data from aconfiguration bit stream into data registers according to an exemplaryembodiment.

FIG. 7 illustrates an example of a system for configuring columns ofconfiguration elements according to an exemplary embodiment.

FIG. 8 illustrates an example of configuring shift registers amongavailable data registers for configuring a PLD with a configuration bitstream without phantom bits.

FIG. 9 illustrates examples of columns of configuration elements whichmay use different configurations of shift registers.

FIG. 10 illustrates an example of a logic design of a data registerblock according to an exemplary embodiment.

FIG. 11 illustrates an example of a logic design of multiple dataregister blocks configured as shift registers according to an exemplaryembodiment.

FIG. 12 illustrates an example of a system for loading data from aconfiguration bit stream without phantom bits into data register blocksconfigured as shift registers according to an exemplary embodiment.

FIG. 13 illustrates another example of a system for configuring columnsof configuration elements according to an exemplary embodiment.

FIG. 14A illustrates one example of including design information of aPLD in a header portion of a configuration bit stream according to anexemplary embodiment.

FIG. 14B illustrates another example of including design information ofa PLD in a header portion of a configuration bit stream according to anexemplary embodiment.

FIG. 15 is a flowchart illustrating a process flow for configuring dataregisters to program a programmable logic device with a configurationbit stream without phantom bits according to an exemplary embodiment.

FIG. 16 is another flowchart illustrating a process flow for configuringdata registers to program a programmable logic device with aconfiguration bit stream without phantom bits according to an exemplaryembodiment.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

FIG. 1 is an example of a schematic of a programmable logic device (PLD)that may be configured with a configuration bit stream. In animplementation, PLD 100 includes a plurality of columns arranged across2 rows. Each column may contain a certain resource type. For example, inFIG. 1, DSP Column 130 may contain a plurality of resources, eachcorresponding to a digital signal processing (DSP) module.

In an implementation, LAB Column 140 may also contain a plurality ofresources, each corresponding to a different resource type than DSPColumn 130. LAB Column 140 may contain a plurality of logic array blocks(LABs), wherein each individual LAB contains a plurality of logicelements which may implement a variety of functions and/or routing. Forexample, in FIG. 1, LAB Column 140 may further include 7 LAB blocks,including LAB 150.

PLD 100 may also include Data Registers 110 along a vertical axis, andAddress Registers 120 along a horizontal axis. In variousimplementations, the locations and orientations of Data Registers 110and Address Registers 120 may be different. For example, Data Registers110 may be oriented along the left or right sides of the PLD rather thanthrough the middle and Address Registers 120 may be on the top or bottomsides of the PLD rather than through the middle of the PLD. In animplementation, the Data Registers 110 and Address Registers 120 may beswitched such that Data Registers 110 is oriented along the horizontalaxis and Address Registers 120 is oriented along the vertical axis.

Accordingly, Data Registers 110 and Address Registers 120 may bevisualized as providing a coordinate system throughout the PLD. Forexample, in FIG. 1, Data Registers 110 may provide y-coordinates andAddress Registers 120 may provide x-coordinates. In variousimplementations, the coordinate system may include the core or array ofthe PLD as well as periphery circuitry (e.g., I/Os, PLLs, etc.), memorydevices (e.g., SRAM units on a PLD), etc. Accordingly, a variety oflocations within the PLD may be addressed via the coordinate systemprovided by Data Registers 110 and Address Registers 120. The locationsmay correspond to configuration elements which may need to be programmedor configured in order to implement specific functionalities within thePLD.

However, in an implementation, not all of the locations provided by thecoordinate system may be utilized. For example, a subset of thelocations provided by the coordinate system may correspond withconfiguration elements such as configuration random access memory (CRAM)cells, which are configured to provide specified functionality, within aPLD. But, not all of the address locations provided by the coordinatesystem may correspond to a CRAM cell due to design considerations suchas physical design issues (e.g., design, locations, sizes, design rules,etc. regarding metal layers, vias, contacts, and other elements of aphysical layout design).

For example, referring back to LAB 150 of FIG. 1, a plurality of AddressLocations 180 may correspond to LAB 150. The address locations, eachrepresented by an empty circle such as Address Location 160, areavailable at all x,y coordinates. However, not all of the addresslocations correspond to a physical CRAM cell. LAB Physical Bits 190illustrates a distribution of physical CRAM cells within LAB 150. LABPhysical Bits 190 shows that LAB 150 includes columns of CRAM cells.Physical CRAM cells, each represented by a solid circle such as CRAMcell 170, may be a subset of Address Locations 180. As such, severaladdress locations do not correspond to an existing CRAM cell for LAB150.

Additionally, in some implementations, different resource types (i.e.,different types of modules such as DSP Modules, LAB Modules, memorymodules, I/Os and other periphery circuitry, etc.) may have a differentdistribution of CRAM cells. FIG. 2 illustrates an example of thedistribution of CRAM cells for DSP Column 130, which differs from thedistribution of CRAM cells for LAB Column 140, as previously described.In FIG. 2, DSP Column 130 of FIG. 1 may include a plurality of DSPmodules, including DSP Module 210. As previously discussed, DSP Module210 also has a plurality of Address Locations 180 corresponding to thecoordinate system provided by Data Registers 110 and Address Registers120. DSP Physical Bits 220 illustrates a distribution of physical CRAMcells within DSP Module 210. DSP Physical Bits 220 shows that DSP 210includes columns of CRAM cells. Physical CRAM cells, each represented bya solid circle such as CRAM cell 170, are also a subset of AddressLocations 180. Just as with LAB 150 of FIG. 1, DSP Module 210 also hasseveral address locations which do not correspond to an existing CRAMcell. However, the distribution of CRAM cells within DSP Module 210differs from the distribution of CRAM cells within LAB 150.

Thus, in one implementation as shown in FIG. 3A, PLD 100 may include a“sea” of coordinates or address locations, such as Address Location 160,the coordinates or address locations provided by Data Registers 110 andAddress Registers 120.

Additionally, in one implementation as shown in FIG. 3B, a subset of thecoordinates or address locations are associated with physically-existingCRAM cells, such as CRAM cell 170. Moreover, each column may have adifferent distribution of physically-existing CRAM cells due to columnscontaining different resource types. For example, in the simplifiedimplementation of FIG. 3B, Column 310 may include one type of resourcetype, such as DSP Modules, while Column 320 may contain a different typeresource type, such as LAB Modules. Because DSP Modules and LAB moduleshave different functionalities and physical layouts, the distribution ofphysically-existing CRAM cells within each of these resource types alsodiffers. As such, Column 310 has a different distribution of CRAM cellsthan Column 320.

Thus, a coordinate system of a PLD has more address locations thanactual CRAM cells. Additionally, different resource types utilizedwithin the PLD may have different distributions of physical CRAM cells.

FIG. 4 is another example of a schematic of a programmable logic device(PLD) that may be configured with a configuration bit stream. In animplementation, PLD 400 also includes a plurality of columns arrangedacross 2 rows. Each column may contain a certain resource type. Forexample, in FIG. 4, DSP Column 460 may contain a plurality of resources,each corresponding to a digital signal processing (DSP) module. LABColumn 430 may also contain a plurality of resources, each correspondingto a Logic Array Block (LAB).

PLD 400 may also include Hard Intellectual Property (IP) Block 410 andHard IP Block 450. Hard IP Blocks 410 and 450 may include a variety ofhard, or hardened or hardwired, functionality. For example, Hard IPBlocks 410 and 450 may include microprocessors, controllers for avariety of functions, clocking circuitry, memory interfaces, memory,configuration circuitry, or any other type of circuitry. In any case,Hard IP 410 and 450 are generally fixed functionality, rather than userconfigurable such as DSP Modules or LAB modules, within the PLD 400. Assuch, Hard IP 410 and Hard IP 450 may lack user-configurable CRAM cells.Since Hard IP 410 and Hard IP 450 are within the coordinate systemprovided by the Data Registers and Address Registers, they overlap withaddress locations, but lack physically existing CRAM cells associatedwith the address locations.

Additionally, Hard IP Block 410 and Hard IP Block 450 may cause a columnto have a difference in the number and/or arrangement of resourcescompared to another column. In the implementation shown in FIG. 4, HardIP Block 450 is in the top-right quadrant of PLD 400. Hard IP Block 450may occupy a certain area of PLD 400, causing DSP Columns and/or LABColumns to have less DSP Modules or LAB Modules compared to other DSPColumns and LAB Columns. For example, LAB Column 430 may have 7 LABmodules. Likewise, LAB Column 480 may also include 7 LAB modules.However, LAB Column 450 may have a different number and/or arrangementof LAB modules compared to LAB Columns 430 and 460. For example, LABColumn 450 may have 4 rows of LAB modules due to Hard IP Block 450making use of a certain area of PLD 400 that would otherwise beavailable to columns, such as LAB Columns or DSP Columns. Likewise, HardIP Block 410 also makes use of a certain area of PLD 400, causing acolumn, such as LAB Column 420, to also have a different number and/orarrangement of LAB Modules. In the implementation of FIG. 4, LAB Column420 may have 3 LAB Modules due to Hard IP Block 410 occupying area ofPLD 400.

Thus, a coordinate system of a PLD has more address locations thanactual CRAM cells. Additionally, different resource types utilizedwithin the PLD may have different distributions of physical CRAM cells.Moreover, fixed functionality, such as hard IP blocks, may cause acolumn to have a different number and/or arrangement of resources. Assuch, a configuration bit stream, which is used to configure a device byindicating how to configure the CRAM cells within the PLD, may include aplurality of bits corresponding to address locations which do not havecorresponding physical CRAM cells.

Accordingly, a configuration bit stream may be shortened or reduced suchthat “phantom bits” which do not correspond to physical CRAM cells maybe removed instead of retaining a “dummy” or filler bit.

FIG. 5 illustrates an implementation of removing phantom bits from aconfiguration bit stream which do not correspond to actual physical CRAMcells on a PLD. In FIG. 5, Original Bit Stream 500 may include fifteenbits. The 15 bits of Original Bit Stream 500 may be divided into threegroups, 510, 520, and 530. Each of the Groups 510, 520, and 530 maycorrespond to a particular group of address locations of the PLD. Forexample, Group 510 may correspond to Addresses 555 of Address Locations550. Group 520 may correspond to Addresses 560. Moreover, Group 530 maycorrespond to Addresses 565.

Additionally, each bit within Original Bit Stream 500 corresponds to aparticular address location. For example, Bit 505 a may correspond withAddress 575 a. Bit 505 b may correspond with Address Location 575 b. Bit505 c may correspond with Address Location 575 c. Bit 505 d maycorrespond with Address Location 575 d. And, Bit 505 e may correspondwith Address Location 575 e. Additionally, Address Locations 575 a, 575b, and 575 e may correspond to physical CRAM cells. Address locations575 c and 575 d may not correspond to physical CRAM cells.

As such, the size of a configuration file may be reduced because bitswhich do not correspond to physical CRAM cells may be removed fromOriginal Bit Stream 500 because the data at the corresponding locationswithin Original Bit Stream 500 are not used to configure a CRAM cell.For example, the “0” represented by 505 c and the “0” represented by 505d do not configure a physical CRAM cell, and are thus phantom bits.However, the “0” represented by 505 a, “1” represented by 505 b, and “0”represented by 505 e may be used to configure physical CRAM cells.

Accordingly, Reduced Configuration Bit Stream 580 may be generated.Reduced Configuration Bit Stream 580 includes 5 less bits than OriginalBit Stream 500 by not retaining the phantom bits. In particular, thebits corresponding to address locations without corresponding physicalCRAM cells are missing. For example, for Group 510, bits 505 c and 505 dare missing because, as previously discussed, Address Locations 575 cand 575 d do not have corresponding physical CRAM cells and thus, thesebits are phantom bits. Accordingly, Group 585 of Reduced ConfigurationBit Stream 580 represents the data included in Group 510 of Original BitStream 500 that have corresponding physical CRAM cells. Group 590includes all of the bits of Group 520 because Addresses 560 of theAddress Locations 550 has every address location corresponding to aphysical CRAM cell. Additionally, Group 595 only has two bits instead offive as represented by Group 530 because Column 565 of Address Locations550 only has two address locations that correspond with physical CRAMcells.

FIG. 6 shows a schematic of an implementation of a system for loadingdata from a configuration bit stream into data registers. In FIG. 6,System 600 includes Configuration Bit Stream Source 610, Control Block620, and Shift Registers 630 and 640. Shift Registers 630 and 640 mayform Data Registers used to configure configuration elements within thePLD, as previously discussed. For example, Shift Registers 630 and 640may be components of Data Registers 110 of FIG. 1.

Configuration Bit Stream Source 610 may provide a configuration bitstream to an input of Control Block 620. Control Block 620 may provideportions of the received configuration bit stream to the first registers(i.e., Registers A and D) of Shift Registers 630 and 640. ShiftRegisters 630 and 640 may be components of Data Registers 110, and thuseach register may drive a data line which is used, in conjunction withaddress lines (not shown) corresponding to Address Registers, toconfigure configuration elements within the PLD. For example, an outputof Register A of Shift Register 630 drives Data Line 0. Register Bdrives Data Line 1, and Register C drives Data Line 2. Likewise, theregisters of Shift Register 640 also drive data lines. Register D drivesData Line 3, Register E drives Data Line 4, and Register F drives DataLine 5.

In some implementations, portions of the configuration bit stream may beprovided to Control Block 620 in parallel. For example, ConfigurationBit Stream Source 610 may drive a 32-bit bus as an input to ControlBlock 620. Control Block 620 may further drive 32 shift registers whichcompose the Data Registers by providing the data from the receivedconfiguration bit stream. In other implementations, Control Block 620may receive data in a 128-bit bus and provide the data via a 32-bit busto 32 shift registers forming the data registers. In anotherimplementation, Control Block 620 may receive data from theConfiguration Bit Stream Source 610 serially. Accordingly, data from theConfiguration Bit Stream Source 610 is received by Control Block 620.Control Block 620 may send portions of the received data to ShiftRegisters 630 and 640 to be driven on Data Lines 0-5. As such, groups ofdata (i.e., bits) from the configuration bit stream may be shifted intoShift Registers 630 and 640 and used to configure columns of CRAM cells.

FIG. 7 shows a schematic of a system for configuring columns ofconfiguration elements according to an implementation. In FIG. 7, system700 includes Shift Registers 630 and 640, Inputs 770 and 780, and threecolumns of CRAM cells: Column 710, Column 720, and Column 730.

In an implementation, Inputs 770 and 780 may be received from ControlBlock 620. The inputs may be used to load Shift Registers 630 and 640with the proper data to configure the PLD. For example, Column 710includes 6 CRAM cells, each represented by a solid circle. Column 720includes 3 CRAM cells (on Data Lines 0, 1, and 4) and 3 locations whichdo not have corresponding CRAM cells (on Data Lines 2, 3, and 5), eachrepresented by an empty circle. Column 730 includes 4 CRAM cells (onData Lines 1, 3, 4, and 5) and 2 locations without corresponding CRAMcells (on Data Lines 0 and 2). Accordingly, a bit stream may be loadedinto Shift Registers 630 and 640 such that the CRAM cells of a singlecolumn may be configured. In the example of FIG. 7, six bits of aconfiguration bit stream may be loaded at a time. Accordingly, threebits may be loaded into Shift Register 630 and three bits may be loadedinto Shift Register 640. However, a bit stream without phantom bits,such as Reduced Configuration Bit Stream 580 of FIG. 5 may not properlyload Shift Registers 630 and 640 because they are of a fixed length(i.e., three bits), number (i.e., two), and/or location (i.e., ShiftRegister 630 begins at Register A, Shift Register 640 begins at RegisterD).

For example, Column 710 includes 6 CRAM cells. Six bits of data from theconfiguration bit stream corresponding to the CRAM cells of Column 710may be shifted into Shift Registers 630 and 640, each including threebits. Following the loading of the data registers (Shift Registers 630and 640), an Address Line (not shown) corresponding to Column 710 may beasserted such that the CRAM cells within Column 710 may be configured.Next, Column 720 may be configured. Accordingly, data is also shiftedinto the data registers composed of Shift Registers 630 and 640. Column720 includes 3 CRAM cells at locations corresponding to Data Lines 0, 1,and 4 and locations lacking CRAM cells corresponding to Data Lines 2, 3,and 5. Therefore, the first bit shifted into Shift Register 630 may be a“phantom bit,” such as a “0” or a “1,” in the configuration bit streamwhich acts as a padding or dummy bit because Register C is notconfiguring a physical configuration element at Data Line 2 for Column720 (i.e., the location lacks a CRAM cell). Following three clockcycles, the phantom bit may be loaded into Register C while Registers Aand B may be loaded with bits from the configuration bit stream whichare meant to configure physical CRAM cells in Column 720 that are drivenby Data Lines 0 and 1. Likewise, the data shifted into Shift Register640 may also include phantom bits from the configuration bit stream. ForColumn 720, Shift Register 640 may include 2 phantom bits to correspondto the locations on Data Lines 3 and 5. Accordingly, an address line(not shown) corresponding to Column 720 may be asserted such that theCRAM cells within Column 720 may be configured with the values driven onData Lines 0-5 by Shift Registers 630 and 640. Though Registers C, D,and F are driving Data Lines 2, 3, and 5, respectively, the data is notused to configure a CRAM cell because the data lines for Column 720 donot correspond with a physical CRAM cell. Rather, the CRAM cells drivenby Registers A, B, and E on Data Lines 0, 1, and 4, respectively, areconfigured. Column 730 may also be configured in a similar matter. Theportion of the configuration bit stream shifted into Shift Register 630may include two phantom bits (for Registers A and C) and one bitcorresponding to a physical CRAM cell (for Register B). Shift Register640 may include three bits corresponding to physical CRAM cells(Registers D, E, and F). Thus, six bits from the configuration bitstream are loaded at a time to properly load Shift Registers 630 and 640and configure the PLD.

However, a configuration bit stream such as Reduced Configuration BitStream 580 from FIG. 5 may not load Shift Registers 630 and 640 properlybecause it has fewer bits due to the removal of phantom bits. Forexample, a configuration bit stream without phantom bits may only haveone bit for the section of Column 720 configured by Shift Register 640(Data Lines 3-5) rather than three bits for a configuration bit streamwith phantom bits. However, because Shift Register 640 is of a fixedlength (three bits) and drives Data Lines 3-5 (of which Data Line 4corresponds to a physical CRAM cell), Shift Register 640 needs threebits to properly load. Accordingly, the bit corresponding to thephysical CRAM cell at Data Line 4 may need to be the second of threebits shifted into Shift register 640.

FIG. 8 shows an implementation of instantiating shift registers amongavailable data registers for configuring a PLD with a configuration bitstream without phantom bits. In FIG. 8, Column 830 includes a column ofCRAM cells and locations without CRAM cells on Data Lines 0-11. DataRegisters 810 is an implementation of fixed shift registers. DataRegisters 810 includes four shift registers. Each register correspondingto a Data Line may be included in one of the four shift registers.Additionally, inputs from a control block may also be fixed. Forexample, Registers A, D, G, and J of Data Registers 810 receive inputsfor each of the four shift registers.

Data Registers 820 is an implementation of dynamic shift registers usedto implement data registers for configuring a PLD. Data Registers 820includes Registers A-L. Each Register may correspond to one of the DataLines 0-11. However, because Column 830 includes seven locations withCRAM cells (i.e., the locations corresponding to Data Lines 0, 2, 4, 7,9, 10, and 11), shift registers may be dynamically configured amongRegisters A-L to form shift registers among the registers correspondingto the seven locations. In other words, shift registers may beinstantiated or generated to only include registers which drive CRAMcells. In some implementations, the length (e.g., two bits, three bits),input location (e.g., a shift register receiving input from a controlblock at a particular register, such as Registers A, E, and J),registers which form the shift register (e.g., Registers A and C forminga shift register while bypassing Register B), and number (e.g., threeshift registers) may vary depending upon a distribution of configurationelements (e.g., CRAM cells) within the particular column, such as Column830. In the example of FIG. 8 and Data Registers 820, shift registersare configured among the available data registers such that there arethree shift registers: a first shift register with an input at RegisterA, a second shift register with an input at Register E, and a thirdshift register with an input at Register J. Additionally, the firstshift register is two bits in length. The second shift register is alsotwo bits in length. The third shift register is three bits in length.Further, each shift register is configured among the available RegistersA-L by bypassing registers corresponding to locations or data lineswhich do not have configuration elements (e.g., CRAM cells) for Column830. Accordingly, Registers B, D, F, G, and I are skipped when the threeshift registers are configured among Registers A-L. Thus, the firstshift register beginning at Register A bypasses Register B and includesRegister C. The second shift register beginning at Register E bypassesRegisters F and G and includes Register H. The third shift registerbeginning at Register J also includes Registers K and L.

Thus, shift registers may be dynamically configured or generated amongthe available data registers such that registers corresponding tolocations without configuration elements may be skipped. Accordingly,the only data needed in the shift registers may be bits corresponding tothe configuration elements. As such, a configuration bit stream withoutphantom bits, such as Reduced Configuration Bit Stream 580 of FIG. 5,may be used to load data registers and configure a PLD.

FIG. 9 illustrates examples of columns of configuration elements whichmay instantiate shift registers with different configurations. Column910 includes seven CRAM cells and five locations without CRAM cells. Inone implementation, three shift registers may be configured amongavailable data registers, as discussed previously with respect to FIG.8. However, because there are seven CRAM cells and three shiftregisters, an imbalance in regards to the number of bits per shiftregister may occur. For example, with seven CRAM cells and three shiftregisters, two shift registers may be two bits in length and the thirdshift register may be three bits in length. Accordingly, the three-bitshift register may need an extra clock cycle to fully load compared tothe two-bit shift registers. As such, a dummy or filler bit may beshifted into the two bit shift registers in the first clock cycle whilethe first “real” bit (i.e., a bit that corresponds to a physical CRAMcell) is shifted into the third shift register. Accordingly, the tworeal bits may be shifted into the two-bit shift registers in thesubsequent two clock cycles such that the two real bits populate thetwo-bit shift registers. In another implementation, shift registers maybe configured to respond to load or enable signals. Accordingly, acontrol block may assert a load or enable signal for the two-bit shiftregisters after the first clock cycle such that no dummy bit needs to beshifted into the shorter shift registers.

In some implementations, the length of the shift registers may bedetermined based on the number of CRAM cells within a column to beconfigured. The number of bits (e.g., seven bits) may be divided by anumber of shift registers to be configured (e.g., three) to obtain aresult of two with a remainder of one. Accordingly, to make segments asbalanced as possible, a single shift register may be three bits whereastwo shift registers may be two bits in length. As another example, with70 bits corresponding to CRAM cells in a column and 32 shift registers,70 divided by 32 yields 2 with a remainder of 6. Accordingly, 6 out ofthe 32 shift registers may be 3 bits long while the remaining 26 shiftregisters may be 2 bits long. As such, a whole number in the divisionmay provide the number of shift registers with one length (e.g., 26shift registers, each 2-bits in length), while the remainder may providethe number of shift registers with a second length (e.g., 6 shiftregisters, each 3-bits in length). In other implementations, theinstantiations of shift registers may be reversed such that 6 of the 32shift registers may be 2 bits long while the remaining 26 shiftregisters may be 3 bits long.

Column 920 is a representation of another column of CRAM cells within aPLD. A configuration of shift registers for Column 920 may differ fromColumn 910 because of a difference in the distribution of CRAM cells.For example, two shift registers, one 2 bits in length and another 1 bitin length, may be configured to load Column 920. Likewise, Column 930may also use a different configuration of shift registers among theavailable data registers. For example, Column 930 may include four shiftregisters of 3 bits in length each. Accordingly, different columns ofCRAM cells may use different configurations of shift registers (i.e., adifference in number of shift registers, locations of shift registersincluding the input, use of particular registers, and length of shiftregisters) to properly configure the PLD.

In some implementations, the number of shift registers instantiatedamong the data registers may be in multiples of two (e.g., 2, 4, 8, 16,32, etc.). In an implementation, the number of shift registers may beconfigured such that the configuration time for each column of CRAMcells may be the same. Accordingly, with variable or dynamic numbers ofshift registers, one column may utilize 2 shift registers, anothercolumn may use 16 shift registers, and so on.

FIG. 10 shows an implementation of a logic design of a data registerblock which may be used to dynamically generate shift registersaccording to an exemplary embodiment. In FIG. 10, Data Register Block1000 includes an Input Multiplexer (Mux) 1010, Register 1015, and OutputMux 1020.

Input Mux 1010 has two data inputs: Configuration Bit Stream Input 1050and Previous Data Register Block 1060. Configuration Bit Stream Input1050 may be data, such as bits from a configuration bit stream, from acontrol block. Previous Data Register Block 1060 may be an output ofanother Data Register Block. The Select or Control Signal 1040, which isused to determine which input to output, of Input Mux 1010 may also bereceived from a control block. The output of Input Mux 1010 may be aninput to Register 1015 and Output Mux 1020. Additionally, an output ofRegister 1015 may be another input to Output Mux 1020. Moreover, OutputMux 1020 may also have a select or control signal 1030, which may alsobe received from a control block according to an implementation. Anoutput of Output Mux 1020 may drive a Data Line as well as be an inputto a next Data Register Block (e.g., Input 1060 of another Data RegisterBlock).

Thus, in an implementation, the Data Register Block 1000 may beconfigured to select either an input from a previous Data Register Blockor a Control Block. Additionally, the Output Mux 1020 of the DataRegister Block may be configured to select either data from the outputof the Input Mux 1010 or Register 1015 to drive onto the Data Line aswell as transmit to a next Data Register Block. Accordingly, multipleData Register Blocks may be used to dynamically configure shiftregisters.

For example, FIG. 11 is an implementation of a logic design 1100 ofmultiple Data Register Blocks configured as shift registers. LogicDesign 1100 includes four Data Register Blocks, each with an Input Mux,Output Mux, and Register (A-D). Each Data Register Block corresponds toa Data Line. In the example of FIG. 11, a portion of column 1150 hasthree locations with CRAM cells (corresponding to Data Register BlocksA, C, and D) and one location without a corresponding CRAM cell (DataRegister Block B). In an implementation, 2-bit shift registers may beconfigured among the registers of the Data Register Blocks. Accordingly,the Data Register Blocks may be configured to create shift registersthat skip or bypass registers (e.g., Register B) that do not correspondwith a CRAM cell for a particular column.

For example, the control signal to the Input Mux of Register A may be 1because Register A may be the input of a first shift register to beconfigured. Accordingly, a data input (e.g., bits from a configurationbit stream) from the control block may be selected. As such, the datainput from the control block may be an input to Register A and itsOutput Mux. However, because the control signal to the Output Mux is 1,the data output of Register A is selected as the output. Accordingly,the output of the Output Mux is used to drive the first Data Line aswell as an input of the next Input Mux for Register B. The controlsignal for the Input Mux for Register B is 0. Accordingly, the output ofthe first Output Mux is selected as the output of the Input Mux forRegister B rather than data from the control block. However, RegisterB's Output Mux has a control signal of 0. Accordingly, the output ofRegister B's Output Mux may be the output of Register B's Input Mux. Assuch, the output of Register B is skipped or bypassed. The output of theOutput Mux of Register B is received by the next Data Register Block.For example, Register C's Input Mux receives the output of Register B'sOutput Mux. Because Register C is the second bit of the first 2-bitshift register, the data from Register B's Output Mux is selected ratherthan data from the control block. Accordingly, the data is sent toRegister C. The Output Mux of Register C has a control signal of 1,selecting the output of Register C. Accordingly, the output of theOutput Mux of Register C is used to drive a Data Line as well as go toan Input Mux of Register D. However, because Register D corresponds to abeginning of a new 2-bit shift register, the Input Mux of Register D hasa control signal of 1, allowing the data shifted in to be data from thecontrol block rather than Register C. The next register forming thesecond 2-bit shift may follow a similar process as with Registers B andC (i.e., skipping registers which do not correspond to a location with aphysical configuration element until a register which corresponds to aphysical configuration element is available). Thus, two 2-bit shiftregisters were configured among the available registers. Additionally,registers which do not correspond to configuration elements, such asRegister B, were skipped from the shift register data paths. As such, aconfiguration bit stream without phantom bits, such as ReducedConfiguration Bit Stream 580 from FIG. 5, may be used to configure aPLD.

As another example, a data path of the first shift register (composed ofRegisters A and C) is highlighted in FIG. 11. A bit being shifted intothe 2-bit shift register may be an input Register B, but the output ofRegister B is skipped. Thus, the bit may be shifted through Registers Aand C while skipping or bypassing Register B. However, the bit is notshifted into Register D because Register D is a separate 2-bit shiftregister. Thus, a 2-bit shift register composed of Registers A and C maybe configured. A separate 2-bit shift register may begin at Register D.Register B has been excluded from the configured shift registers becauseit does not correspond to a physical CRAM cell for Column 1150. Thus,the CRAM cells of Column 1150 may be configured using a configurationbit stream without phantom bits. Accordingly, different columns of CRAMcells may use different configurations of shift registers (i.e., adifference in number of shift registers, input locations of shiftregisters, use of particular registers, and length of shift registers)to properly configure the PLD.

FIG. 12 is an implementation of a system for loading data from aconfiguration bit stream without phantom bits into Data Register Blocksconfigured as shift registers. In FIG. 12, System 1200 includesConfiguration Bit Stream Source 1210, Control Block 1220, and DataRegisters 1230. Data Registers 1230 include a plurality of Data RegisterBlocks 1000 which may be configured as shift registers, as previouslydiscussed.

Configuration Bit Stream Source 1210 may provide a configuration bitstream to an input of Control Block 1220. Control Block 1220 may have adata input to every Data Register Block (RB A-F), as well as controlsignals to the input and output muxes, as previously discussed.Additionally, every data register block may be chained together (e.g.,the data from an output mux may be an input to the next block's inputmux), as previously discussed. The outputs of each output mux may alsodrive a data line. For example, an output of RB A drives Data Line 0. RBB drives Data Line 1, RB C drives Data Line 2, RB D drives Data Line 3,RB E drives Data Line 4, and RB F drives Data Line 5.

In some implementations, portions of the configuration bit stream may beprovided to Control Block 1220 in parallel. For example, ConfigurationBit Stream Source 1210 may drive a 32-bit bus as an input to ControlBlock 1220. Control Block 1220 may further drive 32 shift registerswhich compose the Data Registers by providing the data from the receivedconfiguration bit stream. In other implementations, Control Block 1220may receive data in a 128-bit bus and provide the data via a 32-bit busto 32 shift registers forming the data registers. In anotherimplementation, Control Block 1220 may receive data from theConfiguration Bit Stream Source 1210 serially. Accordingly, data fromthe Configuration Bit Stream Source 610 is received by Control Block620. Control Block 1220 may send portions of the received data to DataRegisters 1230. Additionally, Control Block 1220 may output controlsignals to the input and output muxes of each Register Block. As such,groups of data (i.e., bits) from the configuration bit stream may beshifted into Data Registers 1230 and used to configure columns of CRAMcells.

In other implementations, the control signals may be set by configuredCRAM cells. For example, each control or select line of the input andoutput muxes may be tied high or low by configured CRAM cells.

FIG. 13 shows a schematic of a system for configuring columns ofconfiguration elements according to an implementation. In FIG. 13,system 1300 includes Data Register Blocks A-F and three columns of CRAMcells: Column 710, Column 720, and Column 730.

In an implementation, shift registers may be dynamically configuredamong RB A-F based on a distribution of CRAM cells of Columns 710-730.For example, Column 710 includes 6 CRAM cells, each represented by asolid circle. Column 720 includes 3 CRAM cells (on Data Lines 0, 1, and4) and 3 locations which do not have corresponding CRAM cells (on DataLines 2, 3, and 5), each represented by an empty circle. Column 730includes 4 CRAM cells (on Data Lines 1, 3, 4, and 5) and 2 locationswithout corresponding CRAM cells (on Data Lines 0 and 2). Accordingly,when configuring a column of CRAM cells, Control Block 1220 mayconfigure RB A-F such that the number, location, use of particularregisters, and length of the shift registers vary based on the column ofCRAM cells. For example, if Column 1330 is being configured, RB A-F maybe dynamically configured. In an implementation, RB A-F may beconfigured to include 2 2-bit shift registers, one shift registerincluding RB B and RB D and a second shift register including RB E andRB F. If configuring Column 1310, in an implementation, three 2-bitshift registers may be dynamically configured among RB A-F. For example,RB A and RB B may be a first shift register, RB C and RB D may be asecond shift register, and RB E and RB F may be a third shift register.Accordingly, RB A-F may be dynamically configured to include shiftregisters based on the distribution of configuration elements (e.g.,CRAM cells) of a column.

FIG. 14A illustrates one implementation of including design informationof a PLD in a header portion of a configuration bit stream. For example,in FIG. 14A, Configuration Bit Stream 1400 includes Header 1405 andConfiguration Bits 1410, 1415, and 1420. Header 1405 may include avariety of data, including information for a control block to determinehow to dynamically configure the Register Data Blocks forming the DataRegisters. In the implementation of FIG. 14A, each of Configuration Bits1410, 1415, and 1420 may be of the same length.

FIG. 14B illustrates another implementation of including designinformation of a PLD in a header portion of a configuration bit stream.For example, in FIG. 14B, Configuration Bit Stream 1450 includes threeHeaders (1455, 1465, and 1475) and three Configuration Bits (1460, 1470,and 1480). The header sections may also include a variety of data,including information for a control block to determine how todynamically configure the Register Data Blocks forming the DataRegisters. In the implementation of FIG. 14B, each header section mayinclude information regarding the configuration bits following theheader. For example, Header 1455 may include information regardingConfiguration Bits 1460. Header 1465 may include information regardingConfiguration Bits 1470. Header 1475 may include information regardingConfiguration Bits 1480. The headers may include information such as thetype of module (e.g., LAB or DSP) and the particular column of CRAMcells within the module (e.g., the first column of CRAM cells within aLAB) that the following configuration bits correspond to. Accordingly,when the header portion is received by the control block, theinformation may be read. The control block may determine informationregarding the following configuration bits (e.g., that the followingbits correspond to a first column of CRAM cells within a LAB module).The control block may also obtain information, either from a headersection of a configuration bit stream or from within the PLD itself(e.g., hardcoded in the control block or elsewhere in the PLD, oraccessed from memory), regarding the distribution of phantom bits forthe particular type of module (e.g., a LAB). In other implementations,information regarding a distribution of bits corresponding to physicalconfiguration elements may be obtained. Accordingly, the Data RegistersBlocks forming the Data Registers may be dynamically configured suchthat the following configuration bits may be properly loaded andconfigure the PLD.

For example, Header 1455 of Configuration Bit Stream 1450 may be read bythe control block. Header 1455 may specify that the followingconfiguration bits correspond to a first column of CRAM cells of a LABmodule. The control block may then obtain information regarding thedistribution of phantom bits within a LAB. For instance, bits 2, 8, and10 may be indicated as phantom bits. The control block may alsodetermine the total number of phantom bits or physical bits. As such,registers which do not correspond to physical configuration elements maybe skipped when configuring the shift registers. Additionally, thecontrol block may also configure the Data Register Blocks by assertingthe proper control signals and data inputs such that shift registers ofa particular length, location, and number are configured. ConfigurationBits 1460 may then be loaded into the configured shift registers.

In some implementations, Configuration Bits 1460, 1470, and 1480 may beof different lengths because phantom bits are missing from ConfigurationBit Stream 1450. Accordingly, the shift registers may be dynamicallyconfigured for each column.

In an implementation, a header section may also include informationregarding the distribution of phantom bits corresponding to thefollowing configuration bits. In other implementations, a first headersection may include the distribution of phantom bits for all types ofresources (e.g., LAB, DSP modules) which may be stored by the controlblock. In other implementations, the header sections may indicate thatthe following configuration bits are a new column, but all of the designinformation, such as the resource type, column number, and distributionof phantom bits may be hardcoded or stored in the PLD.

FIG. 15 shows a flowchart of an example of a method for configuring dataregisters to program a programmable logic device with a configurationbit stream without phantom bits. In method 1500, a configuration bitstream may be received at Block 1510. For example, a reducedconfiguration bit stream (i.e., a bit stream without phantom bits suchas Reduced Configuration Bit Stream 580 of FIG. 5), may be received by acontrol block. Accordingly, at Block 1520, shift registers may bedynamically configured among registers within Data Register Blocks. AtBlock 1530, data may be shifted into the configured shift registers. AtBlock 1540, the method is done.

FIG. 16 shows another flowchart of an example of a method forconfiguring data registers to program a programmable logic device with aconfiguration bit stream without phantom bits. In method 1600, a headersection of a configuration bit stream may be received. As previouslydiscussed, the header section may include information regarding thefollowing configuration bits. The information may be read by a controlblock. For example, the information may include a resource type (e.g.,LAB) and a column number (e.g., the first column of CRAM cells withinthe LAB). Accordingly, the control block may determine a distribution ofconfiguration elements for the following configuration bits (e.g., thefirst column of CRAM cells within a LAB). At Block 1630, shift registersmay be configured. As previously discussed, the shift registers may bedynamically configured with varying lengths, locations, and numbers suchthat the PLD may be programmed with a configuration bit stream withoutphantom bits. As such, registers corresponding to a location without acorresponding configuration element may be skipped. At Block 1640,configuration bits to load into the configured shift registers may bereceived. At Block 1650, the configuration bits may be loaded into theconfigured shift registers. Accordingly, the data to configure a columnof configuration elements such as CRAM cells may be loaded and thecolumn may be configured according to the data in the configured shiftregisters. At Block 1660, a determination is made as to whether theconfiguration bit stream is finished. If there is more data, then thenext header section is read at Block 1610. If the configuration bitstream is finished, then method is done at Block 1600 because all of thecolumns of the PLD have been configured.

Configuring shift registers among available Data Register Blocks may beused in applications beyond configuring a PLD. Any application with usesfor dynamically configured shift registers may use the techniquesdisclosed herein.

What is claimed is:
 1. A method for configuring a configurable circuit,the method comprising: receiving on the configurable circuit data from aconfiguration bit stream; instantiating on the configurable circuit afirst shift register among a plurality of registers; instantiating onthe configurable circuit a second shift register among the plurality ofregisters; and sending on the configurable circuit the data from theconfiguration bit stream into the first shift register and the secondshift register.
 2. The method of claim 1, wherein an input to a firstregister of the first shift register is an output of a firstmultiplexer, the first multiplexer configured to output data obtainedfrom the configuration bit stream.
 3. The method of claim 1, whereinregisters among the plurality of registers of the first shift registercorrespond to locations in the configurable circuit with configurationelements.
 4. The method of claim 1, wherein a data path of the firstshift register bypasses a register corresponding to a location in theconfigurable circuit without a configuration element.
 5. The method ofclaim 1 further comprising reading header information of theconfiguration bit stream.
 6. The method of claim 5, wherein the headerinformation is used to instantiate the first shift register and thesecond shift register.
 7. The method of claim 5, wherein the headerinformation includes a resource type and a column number ofconfiguration elements corresponding to the resource type.
 8. The methodof claim 1, wherein a control block instantiates the first shiftregister by determining a distribution of locations withoutcorresponding configuration elements.
 9. The method of claim 1, whereina first portion of a configuration bit stream has a differentinstantiation of shift registers than a second portion of theconfiguration bit stream.
 10. The method of claim 1, whereininstantiating the first shift register includes determining a length ofthe first shift register.
 11. A circuit for configuring a configurablecircuit, the circuit comprising: an input, the input configured toreceive data from a configuration bit stream; a control block, thecontrol block configured to instantiate a first shift register among aplurality of registers and a second shift register among the pluralityof registers; and an output, the output configured to send the data fromthe configuration bit stream into the first shift register and thesecond shift register.
 12. The circuit of claim 11, wherein an input toa first register of the first shift register is an output of a firstmultiplexer, the first multiplexer configured to output data obtainedfrom the configuration bit stream.
 13. The circuit of claim 11, whereinregisters among the plurality of registers of the first shift registercorrespond to locations in the configurable circuit with configurationelements.
 14. The circuit of claim 11, wherein a data path of the firstshift register is configured to bypass a register corresponding to alocation in the configurable circuit without a configuration element.15. The circuit of claim 11, wherein the control block is configured toread header information of the configuration bit stream.
 16. The methodof claim 15, wherein the header information is used to instantiate thefirst shift register and the second shift register.
 17. The method ofclaim 11, wherein the control block is configured to instantiate thefirst shift register by determining a distribution of locations withoutcorresponding configuration elements.
 18. The method of claim 11,wherein a first portion of a configuration bit stream has a differentinstantiation of shift registers than a second portion of theconfiguration bit stream.
 19. The method of claim 11, wherein thecontrol block is configured to instantiate the first shift register bydetermining a length of the first shift register.
 20. A circuit forconfiguring a configurable circuit, the circuit comprising: means forreceiving data from a configuration bit stream; means for instantiatinga first shift register among a plurality of registers; means forinstantiating a second shift register among the plurality of registers;and means for sending the data from the configuration bit stream intothe first shift register and the second shift register.